1. Field of the Invention
This invention relates to the field of scratch-off coatings for concealing information on forms such as lottery tickets, promotional forms, contest forms and the like, and in particular to a scratch-off coating composition in the form of a water based dispersion of acrylic latex and an opaque pigment, and methods for preparing and applying the coating composition.
2. Prior Art
It is known to print indicia on gaming forms such a lottery tickets, promotional forms and the like, which indicia is covered by an opaque scratch-off coating when the form is issued to the player. The coating must be sufficiently opaque to dependably conceal the indicia which may represent a winning ticket, and must be readily removable so that the player can read the information. The scratch-off coating can be a mixture of resin, rubber, solvent and pigment. When the coating is applied the solvent evaporates quickly and the pigment remains. A release coating such as clear varnish or pigmented varnish ink is applied to the form before the scratch-off coating is applied, and preferably over the indicia to be hidden. The release coating allows the player to remove the opaque cover coating by scratching the form with a fingernail, coin or the like.
Solvents in general present environmental and health dangers to humans. The solvents can be ingested by skin contact, by inhalation of vapors, etc. It is virtually unavoidable that workers in the field of solvent printing processes will become exposed to the solvents. Exposure to solvents is widely believed to increase the risk of cancer in humans. Assuming that those involved in the printing process avoid exposure by use of protective equipment, it is still a problem that waste materials, residual solvents in containers, solvents needed to clean operating apparatus, etc., often find their way into the environment. Over time, a facility which regularly handles solvents and materials prepared with, cleaned with or otherwise exposed to solvents, will accumulate potentially dangerous levels.
Known scratch-off coatings which use solvents typically include thermoplastic rubber and a pigment, providing a rubbery consistency for the coating, which is easily applied and readily scratched off. Whereas solvents are undesirable components for environmental reasons, it would be advantageous to provide a comparable coating material with a less dangerous carrier, which would still provide the desirable rubbery consistency, opacity, and ease of application.
Industry has attempted to develop coating products in general, including paints, inks and the like, which are carried in water rather than solvent. However, problems are encountered in attempting to provide a water based scratch-off ink, for example to be used for removably concealing information on lottery tickets, promotional forms and the like. Metallic pigments such as aluminum particles react in water to evolve hydrogen gas, a potential explosion problem. Water based acrylic resins also tend to form a film, which is undesirable in a printing process. It is difficult to provide a water based formulation which is relatively soft and rubbery, for easy scratch-off qualities, but is not tacky when dry or prone to build up on the printing head. For these and other reasons, an effective water based scratch-off ink has not heretofore been available.